1. Field
Example embodiments relate to semiconductor devices, and more particularly, to semiconductor devices having reduced dislocation density and tensile stress.
2. Description of the Related Art
Many nitride-based semiconductor devices use a sapphire substrate. However, a sapphire substrate is costly, difficult to use in manufacturing chips, and has a lower electric conductivity. Also, a larger sized sapphire substrate may not be easily manufactured due to its warpage at a higher temperature and due to its lower heat conductivity in an epitaxial growing process. In order to prevent or reduce the above problems, nitride-based semiconductor devices using a silicon (Si) substrate instead of a sapphire substrate are being developed. Because a Si substrate has a higher heat conductivity than that of a sapphire substrate and thus does not warp as much at a higher temperature for growing a nitride thin film, a larger thin film may grown on the Si substrate.
However, when a nitride thin film grows on a Si substrate, a dislocation density may be increased due to a mismatch of lattice constants and cracks may be generated due to a mismatch of thermal expansion coefficients between the nitride thin film and the Si substrate. As a method of reducing a dislocation density, islands may be grown by using a SiNx dislocation reduction layer and then may be coalesced. However, because tensile stress is additionally generated while the islands are coalesced, a dislocation density may be reduced while cracks are increased. As described above, reducing both a dislocation density and cracks is difficult when a nitride thin film grows on a Si substrate that is vulnerable to tensile stress.